Engine assemblies may incorporate the use of turbochargers to compress the air flowing into the engine to provide a greater amount of air to each cylinder. In order to compress the air flow into the engine, the turbocharger uses exhaust flow from the engine to spin a turbine, which in turn spins an air pump (or compressor). Many turbochargers are provided with a wastegate which acts as a valve to divert exhaust gases away from the turbine wheel in a turbocharged engine system in order to regulate the turbine speed. The wastegate is usually controlled by an actuator. The wastegate is normally closed and is held shut by the actuator. When a preset pressure limit is exceeded, the actuator progressively opens the wastegate allowing exhaust flow to bypass the turbine, thus regulating manifold boost pressure. A turbocharger wastegate actuator is selected or engineered for specified boost level and turbine inlet pressure.
In transient and steady state operation of compressors, there are known noise, vibration, and harshness (NVH) issues characterized by a whoosh noise, or simply whoosh. The turbocharger may therefore cause undesirable or unacceptable levels of NVH. In one particular region of the turbocharger, the wastegate traditionally experiences issues with noise resulting from air flowing out of the wastegate opening particularly when the wastegate door opens and closes.
Attempts have been made to mitigate noise from turbochargers. One attempt to mitigate noise is disclosed in US Patent publication 2010/0098532 to Diemer et al. This reference attempts to reduce turbocharger stall noise by providing a groove that straddles a leading edge of splitter blades of the compressor. The groove is located downstream from a leading edge of main blades to provide a path for fluid around a rotating stall. However, this groove is intended to address noise generated from the compressor wheel.
Other attempts to minimize turbocharger noise have provided various re-circulation passages wherein part of the flow is re-circulated from a downstream position to an upstream position via a passage separate from a main flow passage. An example of such an approach is disclosed in U.S. Pat. No. 7,942,625 to Sirakov et al. Sirakov provides a bleed passage downstream from a blade leading edge that enables a portion of fluid flowing through the compressor to re-circulate to an upstream location via an internal cavity and injection passage. However, similar to US Patent publication 2010/0098532, the aforementioned solution is directed to noise generated from the compressor wheel.
Accordingly, there is a need to reduce noise generated from the wastegate of a turbocharger.